Session initiation protocol (SIP) is a signaling protocol used for establishing sessions in an internet protocol (IP) network. SIP is an Internet Engineering Task Force (IETF)-defined signaling protocol and is widely used for controlling communication sessions such as voice and video calls over IP. A SIP conference session is an association of SIP user agent devices (i.e., conference participant devices) with a central device (i.e., a conference focus device). The conference focus device is the center of the conference. All participant devices in the SIP conference session are connected to the conference focus device by a SIP dialog. The conference focus device has direct peer-wise relationships with the participant devices by maintaining a separate SIP dialog with each participant device. The conference focus device can be implemented either by a participant device or by a separate application server. A session could be as simple as a two-way telephone call, or it could be a complex and collaborative multi-media conference session. Sessions may consist of one or several media streams. The ability to establish these sessions enables a variety of innovative services such as voice-enriched ecommerce, video calls, webpage click-to-dial, and instant messaging (IM) with buddy lists.
A conference session usually includes a host, who organizes or leads the session, and a number of other invitees, also called guests. The host may often have additional privileges beyond those of the guests, such as, for example, being able to add or remove guests from the session. The host may be distinguished from the guests by login information, or by a participant code that is different from any of the participant codes assigned to the guests.
The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of satellites placed in orbit. GPS satellites circle the Earth and continually transmit messages to Earth that include the time the message was transmitted and the satellite position at the time of the message transmission. A GPS receiver uses the messages it receives from multiple satellites to determine the transit time of each message to calculate the location of the GPS receiver.